In the automotive industry, relays have been used to provide a switched connection between components and the battery of a vehicle. In the past, relays did not drain the battery when components were switched off.
With the desire to remove the relay and to have components directly connected to the battery, typically a microcontroller is used to control components such as switches. A problem with such an arrangement is that high side switches (switches connected to the battery), have a control circuit also supplied by the battery. In general the control circuit requires a small dc current to bias some components and this always gives rise to a small but finite standby current drawn by these components when they are switched off.
There is a need to decrease battery drain, and it is therefore desired to reduce standby current, without increasing the number of discrete components again by reverting to relays.
Furthermore automotive manufacturers continue to increase the number of electrically powered devices provided in a vehicle, thereby increasing the number of components which are directly connected to the battery. This compounds the current drain, making the problem even worse.
This invention seeks to provide a control circuit which mitigates the above mentioned disadvantages.